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How is acute myeloid leukemia classified?

Most types of cancer are staged using a number based on the size of the tumor and how far it has spread. But leukemia is not staged in this way because it does not usually form a tumor. It already involves all the bone marrow and, in many cases, it has also spread to other organs. So the outlook for the patient with acute myeloid leukemia (AML) depends on other things, such as the exact type of AML, the age of the patient, and lab test results.

Classification systems

Two systems have been used to classify AML into subtypes -- the French-American-British (FAB) system and the newer World Health Organization (WHO) system.

The French-American-British (FAB) classification of AML

In the 1970s, a group of French, American, and British leukemia experts divided acute myeloid leukemias into subtypes, M0 through M7, based on the type of cell from which the leukemia started and how mature the cells are. This system is based largely on how the leukemia cells looked under the microscope and the symptoms the person has. But now doctors use many advanced gene tests to classify AML.

Prognostic factors

Leukemia treatment has improved, so research has focused on why some patients have a better chance to be cured than others. Differences among patients that affect how they respond to treatment are called prognostic factors. These factors include:

The patient's age

White blood cell count

Certain gene test results

Whether or not the person has had chemotherapy or radiation treatment in the past for another cancer

In recent years, doctors have been using lab tests to learn more about the genetic changes (defects) in AML cells and how they can be used to predict a patient's outlook. These genetic defects might also form the basis for treating the leukemias.

If you would like more details about these prognostic factors, please see the detailed American Cancer Society document, Leukemia: Acute Myeloid (Myelogenous) available through our toll-free number or on our website.

World Health Organization (WHO) Classification of AML

The FAB system described above is useful and is still the one most often used to group AML into subtypes. But it doesn't take into account many of the prognostic factors. The World Health Organization (WHO) has proposed a newer system that includes some of these factors to try to help better classify cases of AML based on a patient's outlook. Not all doctors use this new system.